The present invention relates to systems for tissue characterization based on impedance measurement at a point or at an array of points.
The measurement of electrical potentials on the skin has many uses. For example, electrocardiograms are derived from measuring the potential generated by the heart of a patient at various points on the skin.
Skin potentials are also measured in apparatus for determining the electrical impedance of human tissue, including two-dimensional (e.g., U.S. Pat. Nos. 5,063,937, 4,291,708 and 4,458,694) or three-dimensional (e.g., U.S. Pat. Nos. 4,617,939 and 4,539,640) mapping of the tissue impedance of the body. In such systems an electrical potential is introduced at a point or points on the body and measured at other points at the body. Based on these measurements and on algorithms which have been developed over the past several decades, an impedance map or other indication of variations in impedance can be generated.
U.S. Pat. Nos. 4,291,708 and 4,458,694 and xe2x80x9cBreast Cancer screening by impedance measurementsxe2x80x9d by G. Piperno et al. Frontiers Med. Biol. Eng., Vol. 2, pp 111-117, the disclosures of which are incorporated herein by reference, describe systems in which the impedance between a point on the surface of the skin and some reference point on the body of a patient is determined. These references describe the use of a multi-element probe for the detection of cancer, especially breast cancer, utilizing detected variations of impedance in the breast.
In these references a multi-element probe is described in which a series of flat, stainless steel, sensing elements are mounted onto a PVC base. A lead wire is connected between each of these elements and detector circuitry. Based on the impedance measured between the elements and a remote part of the body, signal processing circuitry determines the impedance variations in the breast. Based on the impedance determination, tumors, and especially malignant tumors, can be detected.
The multi-element probe is a critical component in this system and in other systems which use such probes. On one hand the individual elements must make good contact with the skin and with the corresponding points on the sensing or processing electronics while also being well isolated from each other. On the other hand, use of gels to improve skin contact carries the risk of cross-talk, dried gel build-up on the elements and. inter-patient hygienic concerns.
A paper titled xe2x80x9cCapacitive Sensors for In-Vivo Measurements of the Dielectric Properties of Biological materialsxe2x80x9d by Karunayake P.A.P. Esselle and Stanislaw S. Stuchly (IEEE Trans. Inst and Meas. Vol. 37, No. 1, p. 101-105) describes a single element probe for the measurement of in vivo and in vitro measurements of the dielectric properties of biological substances at radio and microwave frequencies. The sensor which is described is not suitable for impedance imaging.
A paper entitled xe2x80x9cMessung der elektrischen Impedance von Organen-Apparative Ausrxc3xcstung fxc3xcr Forschung und klinishe Anwendungxe2x80x9d by E. Gersing (Biomed. Technik 36 (1991), 6-11) describes a system which uses single element impedance probes for the measurement of the impedance of an organ. The device described is not suitable for impedance imaging.
A Paper titled xe2x80x9cMESURE DE L""IMPEDANCE DES TISSUS HEPATIQUELES TRANSFORMES PAS DES PROCESSUS LESIONELSxe2x80x9d by J. Vrana et al. (Ann. Gastroentreol. Hepetol., 1992, 28, no. 4. 165-168) describes a probe for assessing deep tissue by use of a thin injection electrode. The electrode was positioned by ultrasound and specimens were taken for cytological and histological assessment. The electrode was constituted on a biopsy needle used to take the samples.
A paper titled xe2x80x9cContinuous impedance monitoring during CT-guided stereotactic surgery: relative value in cystic and solid lesionsxe2x80x9d by V. Rajshekhar (British Journal of Neurosurgery (1992) 6, 439-444) describes using an impedance probe having a single electrode to measure the impedance characteristics of lesions. The objective of the study was to use the measurements made in the lesions to determine the extent of the lesions and to localize the lesions more accurately. The probe is guided to the tumor by CT and four measurements were made within the lesion as the probe passed through the lesion. A biopsy of the lesion was performed using the outer sheath of the probe as a guide to position, after the probe itself was withdrawn.
A paper titled xe2x80x9cRigid and Flexible Thin-Film Multi-electrode Arrays for Transmural Cardiac Recordingxe2x80x9d by J. J. Mastrototaro et al. (IEEE TRANS. BIOMED. ENG. Vol. 39, No. 3, March 1992, 271-279) describes a needle probe and a flat probe each having a plurality of electrodes for the measurement of electrical signals generated in the heart.
A paper entitled xe2x80x9cImage-Based Display of Activation Patterns Derived from Scattered Electrodesxe2x80x9d by D. S. Buckles et al. (IEEE TRANS. BIOMED ENGR. Vol. 42, No. 1, January 1995, 111-115) describes a system for measurement of electrical signals generated on the heart by use of an array of electrodes on a substrate. The heart with the electrodes in place is viewed by a TV camera and an operator marks the positions of the electrodes on a display. The system then displays the heart (as visualized prior to the placement of the electrodes) with the position markings.
A paper entitled xe2x80x9cDevelopment of a Multiple Thin-Film Semimicro DC-Probe for Intracerebral Recordingsxe2x80x9d by G. A. Urban et al. (IEEE TRANS. BIOMED ENGR. Vol. 37, No. 10, October 1990, 913-917) describes an elongate alumina ceramic probe having a series of electrodes along its length and circumference for measuring functional parameters (electrical signals) in the brain. Electrophysiological recording, together with electrostimulation at the target point during stereotactic surgery, was performed in order to ensure exact positioning of the probe after stereotactic calculation of the target point. Bidimensional X-Ray imaging was used in order to verify the exact positioning of the electrode tip.
It is an object of certain aspects of the invention to provide a multi-element probe having improved and more uniform and repeatable contact with the skin with minimal operator expertise and minimal risk of cross-patient contamination.
It is an object of certain aspects of the invention to provide improved inter-element electrical isolation, and to permit sliding of the probe while it is urged against the skin.
It is an object of certain aspects of the invention to provide a relatively inexpensive disposable multi-element probe.
It is an object of certain aspects of the invention to provide a multi-element probe having sufficient transparency to allow for viewing of tissue surface features and to allow for referencing the probe with respect to physical features of or on the skin.
It is an object of certain aspects of the invention to provide a method of distinguishing between artifacts and abnormalities.
It is an object of certain aspects of the invention to provide a system for electrical impedance imaging which simultaneously acquires, uses and preferably displays both capacitance and conductance information.
It is an object of certain aspects of the invention to provide a system for electrical impedance testing of the breast or other body region which provides more accurate information regarding the position of impedance abnormalities detected in the breast or other region.
It is an object of certain aspects of the invention to provide for electrical impedance testing with a variable spatial resolution.
It is an object of certain aspects of the invention to provide for two dimensional electrical impedance testing giving an indication of the distance of an abnormality from the surface of the skin.
It is an object of certain aspects of the invention to provide apparatus especially suitable for breast impedance measurements.
It is an object of certain aspects of the invention to provide guidance for placement of elongate objects such as biopsy needles, localization needles, fiber optic endoscopes and the like using real time and/or recorded stereotactic images to guide the object.
It is a further object of certain aspects of the invention to provide a biopsy needle having an impedance measuring function to aid in the taking of a biopsy.
It is an object of certain aspects of the invention to provide more direct comparison between the results of electrical impedance maps and the results of optical, ultrasound or other imaging modalities.
It is an object of certain aspects of the invention to provide apparatus and method for indicating, on an anatomical illustration, the location and region from which an impedance image, shown together with the illustration is derived.
It is an object of certain aspects of the invention to provide apparatus which facilitates direct comparison between X-Ray and impedance mammographic images, as for example by superposition of the images.
It is an object of certain aspects of the invention to provide a method of determining a polychromic (multi-frequency) impedance map.
It is an object of certain aspects of the invention to optimize the impedance mapping utilizing a pulsed voltage excitation.
It is an object of certain aspects of the invention to provide palpation and tactile sensing of an area while simultaneously providing an impedance image of the area.
It is an object of certain aspects of the invention to allow for the identification of tissue types from impedance maps.
In general, the term xe2x80x9cskinxe2x80x9d as used herein means the skin or other tissue of a subject.
The present inventor has found that when, in an impedance image, an anomaly is perceived, the type of tissue underlying the position of the anomaly on the image may generally be determined by a characterization procedure which includes the determination of a number of polychromic measures for the anomaly and surrounding non-anomalous tissue and comparison of the measures with ranges of values of individual polychromic measures or their combinations which are characteristic of various types of tissue. It has been found that normal tissue such as breast tissue, nipples and the infra-mammary ridge, ribs and Costo-chondral Junctions and benign hyperplasia can generally be distinguished from cancerous tumors and precancerous atypical hyperplasia. These measures are based on the structure and form of the deviation of the capacitance and conductance of the anomalous portion of the image from that of the surrounding, normal tissue. For those cases where there is some ambiguity between some types of tissue, knowledge of the anatomy of the imaged area or palpation of the area can often remove the ambiguity or additional views can be taken to remove the ambiguity.
In an image the measures are preferably determined by comparing the capacitance or conductance of the anomalous pixels on the image to be characterized with the capacitance or conductance of normative tissue around the mean or median value of the capacitance or conductance, typically in terms of quantified deviation of a given pixel or region from the median in the image, as measured in multiples of the estimated standard deviation or coefficient of variance.
The method is also potentially useful to determine tissue types in situations where either a single impedance probe is used or where the image is small and only anomalous areas are imaged. In these cases the comparison is made between the values of capacitance or conductance measured for the anomalous region as compared to the capacitance or conductance measured for a nearby region known to be normal.
As used herein the term immitance means either the complex admittance or impedance. Furthermore the term polychromic measure is a measure which is based on the immitance or on the real or imaginary part thereof or on a combination of the immitance and/or the real part thereof and/or the imaginary part thereof at a plurality of frequencies, i.e., on the spectrum thereof.
There is therefore provided, in accordance with a preferred embodiment of the invention apparatus for aiding in the identification of tissue type for an anomalous tissue in an impedance image comprising:
means for providing an polychromic immitance map of a portion of the body;
means for determining a plurality of polychromic measures, preferably normalized measures, of an anomalous region of the immitance image; and
a display which displays an indication based on said plurality of polychromic measures.
Preferably the apparatus includes means for providing a map of said polychromic measures and wherein said indication includes a display of a plurality of said maps.
In a preferred embodiment of the invention the display includes an overlay of maps of said polychromic measures.
Preferably the apparatus includes means for matching the values of the plurality of measures with predetermined values of the measures to identify the tissue type of the anomalous tissue.
In one preferred embodiment of the invention the indication is the display of a map of said determined tissue type.
There is further provided, in accordance with a preferred embodiment of the invention, apparatus for determining a tissue type for an anomalous tissue comprising:
means for determining a plurality of polychromic measures of the anomalous tissue; and
means for matching the values of the plurality of measures with predetermined values of the measures to identify the tissue type of the anomalous tissue.
There is further provided, in accordance with a preferred embodiment of the invention, a method of determining a tissue type for tissue in an anomalous region in an immitance image, comprising:
determining a plurality of polychromic measures, preferably normalized measures, of said anomalous region; and
matching the values of the plurality of measures to identify the tissue type of the anomalous region.
There is further provided, in accordance with a preferred embodiment of the invention, a method of determining a tissue type for an anomalous tissue:
determining a plurality of polychromic measures, preferably normalized measures, of the anomalous tissue;
matching the values of the plurality of measures with predetermined values to identify the tissue type of the anomalous tissue.
Preferably, one of the polychromic measures is derived from the sum, over a plurality of frequencies, of the positive deviations of the capacitance of the anomaly from that of typical nonanomolous regions.
Preferably, one of the polychromic measures is derived from the sum, over a plurality of frequencies, of the negative deviations of the capacitance of the anomaly from that of typical nonanomolous regions.
Preferably, one of the polychromic measures is derived from the sum, over a plurality of frequencies, of the positive deviations of the conductance of the anomaly from that of typical nonanomolous regions.
Preferably one of the measures is the integral of the phase or the sum of phase values over a range of frequencies.
Preferably, one of the measures is the difference between the integral of the difference between the phase at a point and the mean or median value of the phase in the image, over a range of frequencies.
Preferably, one of the measures is the derivative of the capacitance curve or its logarithm as a function of frequency, evaluated at a given frequency.
Preferably, one of the measures is the derivative of the conductance curve or its logarithm as a function of frequency, evaluated at a given frequency.
Preferably, one of the measures is a frequency at which the phase of the impedance reaches a specified value, preferably 45 degrees.